title: An inward proton transport using Anabaena sensory rhodopsin.
abstract: ATP is synthesized by an enzyme that utilizes proton motive force and thus nature creates various proton pumps. The best understood proton pump is bacteriorhodopsin (BR), an outward-directed light-driven proton pump in Halobacterium salinarum. Many archaeal and eubacterial rhodopsins are now known to show similar proton transport activity. Proton pumps must have a specific mechanism to exclude transport in the reverse direction to maintain a proton gradient, and in the case of BR, a highly hydrophobic cytoplasmic domain may constitute such machinery. Although an inward proton pump has neither been created naturally nor artificially, we recently reported that an inward-directed proton transport can be engineered from a bacterial rhodopsin by a single amino acid replacement Anabaena sensory rhodopsin (ASR) is a photochromic sensor in freshwater cyanobacteria, possessing little proton transport activity. When we replace Asp217 at the cytoplasmic domain (distance ∼ 15 Å from the retinal chromophore) to Glu, ASR is converted into an inward proton transport, driven by absorption of a single photon. FTIR spectra clearly show an increased proton affinity for Glu217, which presumably controls the unusual directionality opposite to normal proton pumps.
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya, 466-8555, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Kawanabe
authors.forename: Yuji
authors.initials: Y
authors.lastname: Furutani
authors.forename: Kwang-Hwan
authors.initials: KH
authors.lastname: Jung
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D017033:Anabaena / Q000235:genetics / Q000378:metabolism*; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D017494:Proton Pumps / Q000378:metabolism*; D025603:Sensory Rhodopsins / Q000235:genetics / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D050505:Mutant Proteins; D017494:Proton Pumps; D025603:Sensory Rhodopsins